Noise reduction technique for PWM controllers

Abstract

The present invention is for an architecture for an input circuit to a linear circuit having a circuit ground from a linear system having a system ground. The architecture has a linear input signal which is coupled into a current limiting input impedance. The current limiting input impedance is not connected to the system ground. A linear input circuit is coupled to receive the reduced input signal and is coupled to the circuit ground. Accordingly, the analog input to the linear input circuit is a current signal rather than a voltage signal.

What is claimed is: 
     
       1. A linear circuit architecture comprising: a. a first linear circuit having a first ground;   b. a current limiting input impedance coupled in series to receive a linear signal from the first linear circuit for forming a reduced linear signal and further wherein the current limiting input impedance is a resistor which is not connected to the first ground; and   c. a second linear circuit having a second ground and an input circuit coupled to receive the reduced linear signal from the current limiting impedance.   
     
     
       2. The linear circuit architecture according to claim 1 wherein the input circuit comprises a diode having an anode and an NPN transistor having a base coupled to the current limiting impedance and the diode cathode and transistor emitter coupled to the second ground. 
     
     
       3. A linear circuit architecture comprising: a. a first linear circuit having a first ground;   b. a current limiting input impedance coupled in series to receive a linear signal from the first linear circuit for forming a reduced linear signal wherein the linear signal is a current signal; and   c. a second linear circuit having a second ground and an input circuit coupled to receive the reduced linear signal from the current limiting impedance.   
     
     
       4. A linear circuit architecture comprising: a. a first linear circuit having a first ground;   b. a current limiting input impedance coupled in series to receive a linear signal from the first linear circuit for forming a reduced linear signal wherein the reduced linear signal is approximately independent of noise in the first ground or the second ground; and   c. a second linear circuit having a second ground and an input circuit coupled to receive the reduced linear signal from the current limiting impedance.